Convert tags parameter from list to dict in launch_ec2.

There are two big reasons for doing so:
  - It relied on functions that were internal to ansible and whole behavior has now changed.
    The functions to get the extensions and filters from ansible can still be accessed after
    instantiating an object of the Templar class but the way that this loads variables has
    now changed and so we can't do the same sort of tests as we did previously without loading
    the entire variable context for the template file.
  - This test should now be achieved by running the relevant docker builds that test the templates
    can render correctly within the full context they need.

To catch errors faster we may want to add a jinja linter that does the rudimentry syntax checks
without needing to know about the ansible jinja filters and extensions that are available.

These are no longer relevant in newer base images of 12.04 and 16.04

Checking for them is generally a waste of time these days.
We also now default to applying security updates on devstacks and
we do them in production.  We may enable them everywhere in a future
release, but that will require more updates.

ECOM-6570

Upgrade edxapp node version to 6.9 LTS

Remove partially implemented pip-accel code

Remove node ppa from jenkins-worker.

Removing ref to removed requirements file